[RobinP]

I think the quantative her2 testing would naturally be less sensitive in early stage disease as less her2 would theoretically be shed and circulating in the ECD-extracellular domain, the blood.

The problem with her2 serum testing is that it is probably most sesitive at the time of diagnosis- prior or just at tumor removal when her2 is shedding into the serum. If you are testing it late, as you are AA, there probably will be none to minimal levels of her2 unless you have an unknown mets out there that is evidencing itself, pre-clinically before a known mets, by tumor shedding.